Red Dwarfs: The Hidden Majority
When you gaze up at the night sky, the twinkling points of light you see are not just suns like our own. In fact, the majority of stars in our galaxy are smaller red dwarfs, little cosmic underdogs that make up about three out of every four stars. These red dwarfs are nearly half the size of our Sun and have long intrigued astronomers looking for potential habitable worlds. Scientists have set their sights on these stars because their cooler temperatures allow planets to orbit closer without being scorched. This proximity makes them excellent candidates for detecting atmospheres—an essential ingredient for habitability.
The atmospheres of planets hold the key to life as we know it. Earth’s own atmosphere acts as a security blanket, maintaining a stable climate and shielding us from harmful space radiation. While scientists have detected atmospheres around numerous gas giants, discovering a rocky planet with a habitable atmosphere remains elusive. Enter the James Webb Space Telescope (JWST). NASA, alongside its European and Canadian counterparts, has budgeted about 500 hours to observe rocky exoplanets orbiting red dwarf stars. The goal is ambitious but potentially groundbreaking: to confirm whether these planets have atmospheres and what those atmospheres are composed of. “This is one of those high-risk, high-reward programs,” says Néstor Espinoza, an astronomer leading the program’s team. “Imagine that for all of the targets, we detect atmospheres. Then you answer the question, ‘Yes, atmospheres are very common around these stars. That means maybe life can emerge.'”
Jennifer Lotz, who directs operations for both Webb and the Hubble Space Telescope, has initiated a complementary survey using Hubble’s ultraviolet observations. While the JWST will explore the atmospheres, Hubble is tasked with characterizing the activity of the red dwarf stars, which are known to bombard their planets with radiation. The collaborative effort is essential for one significant reason: Webb and Hubble are not rivals but complementary forces. “It’s kind of the perfect dream team to do this job,” Espinoza notes. The two telescopes working in tandem could provide a wealth of data, potentially leading to the discovery of habitable worlds.
Traditionally, astronomers have used transmission spectroscopy to study exoplanet atmospheres. This involves analyzing starlight that passes through a planet’s atmosphere when the planet transits in front of its star. However, red dwarfs are notorious for stellar spots, which can contaminate the signal, making it difficult to discern atmospheric components accurately. The JWST has pivoted to a technique called secondary eclipse spectroscopy. This method involves capturing the signal from both the star and the planet when the planet is beside the star, and then isolating the star’s light when the planet moves behind it. By subtracting the stellar light, researchers can isolate the planet’s atmospheric signature.
NASA’s new campaign will focus on rocky planets, specifically those that range in temperature from 200 to 450 Kelvin. For perspective, Earth sits at a comfortable 288 Kelvin (59 degrees Fahrenheit). The survey aims to include planets less than twice the size of Earth to maximize the chances of finding something truly Earth-like. TRAPPIST-1, one of the most famous red dwarf systems teeming with rocky planets, remains a focal point. Having previously studied some of these planets, astrophysicist Kevin Stevenson from Johns Hopkins Applied Physics Laboratory believes the JWST survey will advance understanding of rocky worlds by a decade. “This survey program will be the next major step towards answering the question, ‘Are we alone?'” he says.
If the survey yields planets with atmospheres, it could redefine the way JWST and other flagship observatories are used in the future. Conversely, if no atmospheres are detected, astronomers might need to shift focus back to planets orbiting sun-like stars, utilizing future instruments like the Habitable Worlds Observatory. “If the program is able to conclusively determine that one of these rocky worlds around an M dwarf star has an atmosphere, it could really set the stage not only for the rest of JWST’s science operating lifetime but also maybe that of the next great observatory,” says Sarah Moran, an exoplanet scientist at the University of Arizona.
The upcoming survey of rocky worlds orbiting red dwarf stars presents one of the most thrilling scientific pursuits of our time. As a tech investor and space enthusiast, watching the JWST and Hubble collaborate to answer the age-old question, “Are we alone?” feels like witnessing history in the making. With the power of cutting-edge technology and collaborative science, we are on the cusp of potentially redefining our place in the universe. Whether we find atmospheres—or even signs of life—around these distant worlds, the journey itself will undoubtedly expand our horizons and deepen our understanding of the cosmos.